1. Field of the Invention
The present invention relates in general to a power transmitting device, and more particularly to improvements of a power transmitting device including a first side gear and a second side gear to which power received from rotary driving means is distributed through a differential case while, so as to permit differential rotation of the first and second side gears.
2. Discussion of the Related Art
There is known a power transmitting device (so-called "parallel axes type differential gear device") comprising: (a) a differential case rotated about a centerline by rotary driving means; (b) a first and a second externally toothed side gear which are disposed within said differential case coaxially with said differential case and rotatably about said centerline; (c) at least one first pinion member disposed rotatably about respective first axes offset from and parallel with said centerline, supported by said differential case so as to be rotated therewith about said centerline, and engaging said first side gears; and (d) at least one second pinion member disposed rotatably about respective second axes offset from and parallel with said centerline, supported by said differential case so as to be rotated therewith about said centerline, and engaging said second side gears and said at least one first pinion member, and wherein power received from the rotary driving means is distributed through the differential case to the first and second side gears, so as to permit differential rotation of the first and second side gears.
An example of the above-indicated type of power transmitting device is disclosed in JP-A-7-506419. During the differential rotation of the first and second side gears, a radial load, or a radial load and a thrust load acts or act on the first and second pinion members due to a load of engagement thereof with the first and second side gears, so that the pinion members are forced against the inner surfaces of the differential case, with a result of generation of a friction force therebetween, which restricts relative rotation of the two side gears, thereby providing a torque sensing type differential limiting effect.
For example, the power transmitting device as described above is constructed as schematically illustrated in FIG. 5. This device includes: a differential case 10 which is rotated about a centerline O by rotary driving means in the form of an engine of an automotive vehicle; a first side gear 12 and a second side gear 14 which are externally toothed gears and which are disposed within the differential case 10 coaxially therewith and rotatably about the centerline O; first pinion members 16 which are disposed rotatably about respective first axes offset from and parallel to the centerline O, supported by the differential case 10 so as to be rotated therewith about the centerline O, and engage the first side gear 12; and second pinion members 18 which are disposed rotatably about respective second axes offset from and parallel with the centerline O, supported by the differential case 10 so as to be rotated therewith about the centerline O, and engage the second side gear 14 and the first pinion members 16. In this power transmitting device, power or torque received by the differential case 10 is distributed to the first and second side gears 12, 14.
The first pinion members 16 are arranged equiangularly in the circumferential direction of the differential case 10 about the centerline O, while the second pinion members 18 are arranged equiangularly in the circumferential direction of the differential case about the centerline O such that each second pinion member 18 is in meshing engagement with the corresponding one of the second pinion members 18. For instance, the first pinion members 16 consist of three first pinions members while the second pinion members 18 consist of three second pinion members meshing with the respective first pinion members 16.
Described in detail, the differential case 10 have pinion holes and support shafts. These pinion holes or pinion support shafts are evenly spaced from each other in the circumferential direction of the differential case 10, so that the first and second pinion members 16, 18 are accommodated in the respective pinion holes and rotatably mounted on the respective pinion support shafts, such that there are left suitable amounts of clearances between the pinion members 16, 18 and the surfaces of the pinion holes and support shafts, so as to give the pinion members 16, 18 some amounts of plays. During differential rotation of the first and second side gears 12, 14, the pinion members 16, 18 are forced against the surfaces of the differential case 10 due to a load of meshing engagement of the pinion members 16, 18 with the side gears 12, 14, and the friction force between the pinion members 16, 18 and the differential case 10 acts to restrict relative rotation of the two side gears. Where the side gears 12, 14 and the pinion members 16, 18 are spur gears, a radial load acts on the pinion members 16, 18, due to the pressure angle, and the top faces or lands of the teeth of the pinion members 16, 18 are forced onto the inner wall surfaces of the pinion holes, etc. Where the side gears 12, 14 and the pinion members 16, 18 are helical gears having twisted tooth traces, a thrust load acts on the pinion members 16, 18, due to the helix angle, and the axial end faces of the pinion members 16, 18 are also forced onto the inner side walls of the differential case 10.
In the example of FIG. 5, the first and second side gears 12, 14 have the same outside diameter, so that the torque is equally distributed to these two side gears 12, 14. However, the two side gears 12, 14 may have different outside diameters to achieve uneven torque distribution.
However, the power transmitting device as shown in FIG. 5 is limited in the positions at which the power is received and transmitted to external members such as drive wheels of a motor vehicle. In a center differential device 20 of a motor vehicle illustrated in FIG. 6, for instance, power generated by an engine 22 as the rotary driving means is received by the center differential device 20 through a transmission 24, and is distributed by the device 20 to front and rear drive wheels of the motor vehicle. To transmit the power from the center differential device 20 to the front drive wheels, a sprocket is disposed between the transmission 24 and the center differential device 20, so that the power is transmitted to the front drive wheels through a chain 26 engaging the sprocket. This type of power transmitting system suffers from a relatively low degree of flexibility in the positions of the power input and outputs. Described more specifically referring back to FIG. 5, the power is received at a radially outer portion of the device, and first and second outputs are provided at the centerline O of the device. In this case, the second output to the front drive wheels cannot be transferred to the chain 26.
On the other hand, the power transmitting device may be adapted to receive the input power at the centerline O, as indicated in FIGS. 7 and 8. In these cases, however, the first output from the first side gear 12 and the second output from the second side gear 14 are both provided on the same axial side (rear or front) of the power transmitting device.
The power transmitting device of FIG. 7 may be modified as shown in FIG. 9. In this modified arrangement, an outer shell 28 is disposed outwardly of the differential case 10, so that the first output to the front drive wheels can be obtained at the front side of the device, through the outer shell 28 via a member splined to the outer shell 28. Similarly, the power transmitting device of FIG. 8 may be modified as shown in FIG. 10. In this modified arrangement, too, an outer shell 30 is disposed outwardly of the differential case 10, so that the second output to the rear drive wheels can be obtained at the rear side of the device, through the outer shell 30 via a member splined to the outer shell 30. However, these modified power transmitting devices suffer from an increased radial dimension and an increased number of components, and are not necessarily satisfactory in the overall evaluation.